President Bush's commitment to defend Saudi Arabia and its oil wealth with American troops springs from a relationship that dates back to World War II and a shipboard meeting between Franklin D. Roosevelt and king Abdulaziz bin Saud, the founder of the modern Saudi dynasty.

Roosevelt met the Saudi monarch in 1945 while returning from the Yalta conference with Joseph Stalin and Winston Churchill. The meeting, aboard a U.S. cruiser in the Suez Canal, came as the United States was beginning to replace Britain as Saudi Arabia's main link to the Western world, and historians believe the encounter hastened that process.

Over the years, the U.S.-Saudi relationship has been unsettled by the Arab-Israeli conflict, but it has remained firmly based on the two countries' central needs -- that of America for Saudi oil and that of Saudi Arabia for U.S. technology and military protection. The relationship frequently included secrecy -- a covert demension that, according to U.S. and Arab analysts, has served both partners.

U.S. oil firms began exploring Saudi Arabia in the 1930s and invested heavily after Standard Oil of California drilled a gusher in 1938. Meanwhile, as Washington built its World War II military machine, it awoke to what British author Robert Lacey called "the realization that America, as the petrol tank of the Allies' war effort, was pumping 63 percent of the world's oil consumption every day from her own reserves."

In 1942, a U.S. government memo identified "the development of Saudi Arabian petroleum resources" as a "broad national interest," and Washington quickly made Lend-Lease aid available to Abdulaziz, providing him with a level of financial support the British had never been able to offer.

In the 1950s, the U.S.-Saudi relationship began to broaden. Burgeoning Saudi oil riches and advancing American technology naturally sought each other, and Riyadh began turning toward the United States to help build military facilities, train its forces and sell it weapons.

The Saudis underwent "a gradual political Westernization as more and more of the Saudi royal family, the grandsons of Abdulaziz, were educated in the United States," said Don Peretz, a Middle East specialist at the State University of New York at Binghamton. That U.S.-educated generation now forms a high-ranking layer of government officials.

The Arab-Israeli conflict has been a constant intrusion in Saudi-U.S. ties but has only occasionally led to confrontation, such as during the Arab oil embargo that followed the Arab defeat in the 1973 war with Israel.

As well, Arab nationalists look dimly upon Arab governments that depend on outside powers for their security, and the Saudi rulers have wanted to distance themselves from the United States specifically because of U.S. support for Israel.

One problem for the Saudis "is that {Americans} talk a lot," said Robert G. Neumann, a former U.S. ambassador to Riyadh. "They would like us to do everything under the table." The Saudis have had trouble understanding America's boisterous democracy and frequently have been embarrassed by public debates over sales to Riyadh of high-technology weapons, such as AWACS surveillance planes and F-15 fighters.

But alongside the necessarily public nature of arms sales, both U.S. and Saudi governments have cooperated secretly on security matters. When the Soviets invaded Afghanistan in 1979, its warplanes gained a base close to the Strait of Hormuz "chokepoint" at which Persian Gulf oil shipments might be cut off. Saudi Arabia and the Reagan administration covertly pooled hundreds of millions of dollars to buy arms for the Afghan mujaheddin rebels.

During a period when the Reagan administration was legally prohibited by Congress from providing military aid to the Nicaraguan rebels, or contras, it arranged for the Saudis to send an estimated $30 million for weapons, according to testimony at last year's Iran-contra trial of Lt. Col. Oliver North.

Saudi Arabia also has aided other conservative, pro-Western Arab governments. Diplomats and other analysts in North Africa long have regarded Saudi financial aid as critical to the stability of King Hassan II of Morocco, perhaps the closest Arab ally of the United States.

But if oil remains the single most important U.S.-Saudi tie -- the United States bought 17 percent of its imported oil from Saudi Arabia in 1988, according to government figures -- it is only part of a more complex commercial relationship. In recent years, Saudi Arabia has ranked as high as ninth in the world as a purchaser of U.S. goods.